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std::rotate() function with example in C++ STL

C++ STL | std::rotate() function: Here, we are going to learn about the rotate() function of algorithm header in C++ STL with example.
Submitted by IncludeHelp, on May 26, 2019

C++ STL std::rotate() function

rotate() function is a library function of algorithm header, it is used to rotate left the elements of a sequence within a given range, it accepts the range (start, end) and a middle point, it rotates the elements in such way that the element pointed by the middle iterator becomes the new first element.

Note: To use rotate() function – include <algorithm> header or you can simple use <bits/stdc++.h> header file.

Syntax of std::rotate() function

    std::rotate(iterator start, iterator middle, iterator end);

Parameter(s):

iterator start – an iterator pointing to the first element of the sequence.
iterator middle – an iterator pointing to the middle or any other elements from where we want to start the rotation.
iterator end – an iterator pointing to the last element of the sequence.

Return value: void – it returns noting.

Example:

    Input:
    vector<int> v{ 10, 20, 30, 40, 50 };
    
    //rotating vector from 2nd element
    rotate(v.begin(), v.begin() + 2, v.end());
        
    Output:
    30 40 50 10 20

C++ STL program to demonstrate use of std::rotate() function

In this program, we have a vector and we are rotating its elements from 2^nd index.

//C++ STL program to demonstrate use of
//std::rotate() function
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

//main code
int main()
{
    //vector
    vector<int> v{ 10, 20, 30, 40, 50 };

    //printing vector elements
    cout << "vector elements begfore rotating..." << endl;
    for (int x : v)
        cout << x << " ";
    cout << endl;

    //rotating vector from 2nd element
    rotate(v.begin(), v.begin() + 2, v.end());

    cout << "vector elements after rotating..." << endl;
    for (int x : v)
        cout << x << " ";
    cout << endl;

    return 0;
}

Output

vector elements begfore rotating...
10 20 30 40 50
vector elements after rotating...
30 40 50 10 20

Reference: C++ std::rotate()